Ecologists increasingly recognize that individual mechanisms often act (and interact) in concert. This research will employ a powerful approach to evaluate the roles of various mechanisms, both individually and in combination, that allow multiple species to coexist. The study system consists of two specialist parasitoids (parasitic insects that attack eggs) of the harlequin bug. Their approach of integrating laboratory and field experiments with theoretical modeling will provide a means for evaluating multiple mechanisms that influence species coexistence. The factors to be evaluated include variability in resources, temporal variation, developmental rates of species, resource use, species interactions such as competition and predation, and the role of temporal refugia. A model will be developed to assess the mechanisms involved in species coexistence, to generate new predictions, and to generalize to other systems. The results of this research will inform real-world models of biological control and provide insight into our understanding of the mechanisms that maintain biodiversity.
The project involves training undergraduates, graduate students and postdoctoral associates in quantitative and experimental approaches to studying ecology. The ability to integrate theory and data is a crucial skill for the next generation of scientists who will tackle the important ecological and environmental issues that confront the nation. The proposed research will provide this training to young researchers at various career stages, emphasizing strong participation by women and other underrepresented groups.
This project investigated the mechanisms by which species within a community interact and coexist in the long-term. These mechanisms involve ameliorating effects of competition for resources and attacks from natural enemies by escaping these effects in time or space. For example, insect parasites (parasitoids) that lay their eggs on other insects (mostly plant-feeding insects called herbivores) may emerge at different times so competition between parasite larvae for their common insect host would be reduced. Another mechanism is dispersal, species that have greater mobility can find food or other limiting resources by moving to different parts of the habitat, thus reducing overlap with their competitors or natural enemies (predators, parasites). Temperature is one of the most important environmental factors that affects populations and communities. Understanding effects of temperature is particularly important given the strong evidence for climate warming and its consequences for biodiversity. The main goal of the project was to investigate how temperature influenced the coexistence of prey or host species that are attacked by multiple natural enemy species where the natural enemy species engage in competition for their common host. We conducted experiments on an insect host-parasitoid community and used the experimental data to build mathematical models that investigated whether differences between species in their responses to temperature (in terms of their reproduction, development and survival) could allow them to coexist over long time periods. We made several important findings. First, we used our experimental data on temperature effects on reproduction, development and survival to predict how the fitness of a species (its net population growth rate, which, if positive, allows the species to persist) is affected by variation in the environmental temperature. Recent studies have suggested that tropical species are more at risk of extinction due to climate warming than temperate species, but do not explain why this would be the case. Our work on the temperature dependence of fitness helps to explain these findings. Tropical species are more at risk of extinction because their development is more sensitive to temperature and they are able to reproduce on a narrower temperature range than temperate species. Thus even a small increase in the environmental temperature could cause them to go extinct. This is an important finding because it suggests that climate warming is likely to cause the most harm in tropical areas, which contain most of the earth's biodiversity. A second important finding is the effects of temperature on invasive pest species that attack economically important crops. In the U.S. and many other parts of the world, pests are controlled using natural enemies (predators and parasites). Biological pest control, either in isolation or combined with an integrated pest management scheme, reduces pesticide use and minimizes pollution of water sources and associated health risks to humans and livestock. Yet, we know very little about how climate warming may affect biological control practices. Our work shows that if pests are better able to withstand or adapt to climate warming than the natural enemies that suppress them, biological control will fail, causing pest outbreaks. If climate warming causes such outbreaks in primarily agricultural states like California and Florida, it is likely to compromise the nation's food supply. Our work identifies attributes of natural enemies that make them more tolerant to climate warming, which could be used as guidelines in developing biological control programs. Our findings have been disseminated through publications in scientific journals and talks at international conferences and workshops. This project has also provided training and mentoring to undergraduate and graduate students and postdoctoral research fellows. A key aspect of this training involves combining controlled experiments with mathematical theory to address questions of ecological and environmental importance. Promoting undergraduate research, particularly to under-represented groups, has been a strong emphasis of this research program. To date, the project has trained over 20 undergraduates more than half of whom conducted Honors research projects. Several students won prestigious research awards at UCLA and two students are authors of papers published in top-tier journals.
